Kim Changgong, Matlack Kathryn H
Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
Ultrasonics. 2023 May;131:106945. doi: 10.1016/j.ultras.2023.106945. Epub 2023 Feb 4.
The acoustic nonlinearity parameter β is sensitive to dislocation parameters, which continuously change during plastic deformation. Dislocation-based damage in structures/components is the source of the failure; thus, β has been studied as a metric for non-destructive evaluation. This work consists of two parts: the development of an in situ experimental setup for nonlinear Rayleigh wave measurements, and characterization of the dependence of β on applied stress at different levels of initial plastic strain. First, we introduce an experimental setup and methods for repeatable in situ nonlinear ultrasonic measurements. Details on design considerations and measurement schemes are provided. In the second part, β was measured in situ during an incremental monotonic tensile test. The measured β monotonically decreases with plastic strain, but it is relatively insensitive to the applied stress during elastic deformation. This result highlights three aspects of the evolution of β, which have not been sufficiently emphasized in prior work: the apparent insensitivity of β to the applied stress during elastic deformation, decreasing β with plastic deformation, and the saturation of β. We attribute the trend of decreasing β to a scaling of β with monopole loop length during plastic deformation, which depends on initial microstructure. The saturation of β at 1.8% coincides with a planar-to-wavy transition of dislocation structures. The in situ nonlinear ultrasonic experimental method presented in this work is significant as the in situ results can provide broader insights on β and dislocation-based damage evolution than ex situ measurements alone.
声学非线性参数β对位错参数敏感，而位错参数在塑性变形过程中会持续变化。结构/部件中基于位错的损伤是失效的根源；因此，β已被作为一种无损评估指标进行研究。这项工作包括两个部分：开发用于非线性瑞利波测量的原位实验装置，以及表征β在不同初始塑性应变水平下对应力的依赖性。首先，我们介绍一种用于可重复原位非线性超声测量的实验装置和方法。提供了设计考虑因素和测量方案的详细信息。在第二部分中，在增量单调拉伸试验过程中对β进行原位测量。测得的β随塑性应变单调降低，但在弹性变形期间对应力相对不敏感。这一结果突出了β演化的三个方面，而这在先前的工作中并未得到充分强调：β在弹性变形期间对应力明显不敏感、β随塑性变形降低以及β的饱和。我们将β降低的趋势归因于塑性变形期间β与单极环长度的比例关系，这取决于初始微观结构。β在1.8%时的饱和与位错结构从平面到波浪状的转变相吻合。这项工作中提出的原位非线性超声实验方法具有重要意义，因为原位结果比单独的非原位测量能提供关于β和基于位错的损伤演化更广泛的见解。
